Automatic stationary rotary tongs



March 20, 1962 N. v. SOODNIZIN 3,025,733

AUTOMATIC STATIONARY ROTARY TONGS Filed July 13, l959 2 Sheets-Sheet las 34 gr INVENTOR lV/O'HOLAS VLAD/M/ROV/TGH SOOD/V/Z/IV ATTORNEYS March20, 1962 N. v. SOODNIZIN AUTOMATIC STATIONARY ROTARY TONGS 2Sheets-Sheet 2 Filed July 13, 1959 v INVENTOR NICHOLAS VLAD/M/ROV/TCHSOOD/V/Z/N Uited States Patent Ofiice 3,025,733 Patented Mar. 20, 19623,025,733 AUTOMATEC STATIONARY RQ'IARY TQNGS Nicholas WadimirovitehSoodnizin, Warsaws Chaussee, 135a, Korpus 2., Apt. 12, Moscow, U.S.S.R.Filed .Iuly 13, 1959, Ser. No. 846,765 Claims. (Cl. 81--53) Thisinvention relates to tools and more particularly to a power drivenrotary tongs primarily intended for turning an upper section of pipe ina pipe string with respect to a lower section in order to couple oruncouple one pipe section to or from the other.

Heretofore many different types of rotary tongs or wrenches have beenproposed and utilized for operating on drill pipe strings or wellcasings in connection with oil wells or other wells where it isnecessary to couple or uncouple relatively large and long pipe sectionsand all of these tools have attempted, in one way or another, toovercome the rather difiicult problem of applying sufficient torque tothe pipe to accomplish the desired result and at the same time, avoidexerting a lateral strain upon the pipe which would tend to bend thesame or move the same out of vertical alignment and numerous types offorce multiplying mechanisms have been proposed for this purpose.

The present invention solves this rather difficult problem by utilizingthe inertia of rotating parts, including a flywheel to supply thenecessary torque and this mechanism permits the use of a relatively lowpower prime mover for driving the mechanism with the result thatsufficient torque for the purpose is developed and without exerting anylateral strain on the pipe string.

It is accordingly an object of the invention to provide a power drivenrotary tong which may be permanently mounted adjacent a pipe string tobe operated upon and moved into or out of operative position inalignment with the pipe string by suitable hydraulic or other powermeans.

A further object of the invention is the provision of a power drivenrotary tongs for rotating one pipe section with respect to another andin which means is provided for holding one pipe section stationary whilerotating the other pipe section with respect thereto.

A still further object of the invention is the provision of a powerdriven rotary tongs for operating upon a pipe string in which means isprovided for engaging and disengaging jaw pieces with one pipe sectionto hold the same stationary, there being means also provided forengaging and dis-engaging other jaw pieces with an upper pipe sectionfor rotating the same with respect to the lower pipe section.

Another object of the invention is the provision of a power drivenrotary tongs for rotating one pipe section with respect to another pipesection and in which power operated means is provided for engaging anddis-engaging jaw pieces with the two pipe sections.

A further object of the invention is the provision of a power drivenrotary tongs for rotating one pipe section with respect to another pipesection, there being a fixed jaw for holding one pipe section stationaryand a rotating driven jaw for rotating the other pipe section, therotating jaw being driven by a gear train which in turn is driven by aprime mover, there also being a flywheel connected to the gear train forimparting torque thereto.

A still further object of the invention is the provision of a powerdriven rotary tongs for rotating one pipe section with respect toanother pipe section and including rotary jaws engaging the pipe sectionto be rotated, the jaws being driven by a gear chain connected to aprime mover and a flywheel and in which means is provided for releasablycoupling the flywheel to the gear chain for limiting or adjusting atorque transmitted thereto from V the flywheel.

Another object of the invention is the provision of a power drivenrotary tongs for rotating one pipe section with respect to another pipesection and in which stop means is provided for stopping the piperotating mechanism at a neutral or predetermined position, such stopmechanism being operated by power driven means.

A further object of the invention is the provision of a power drivenrotary tongs for rotating one pipe section with respect to another pipesection and in which the tongs may be moved into and out of engagementwith the pipe sections and operated to rotate one of the pipe sectionswith respect to the other pipe section without manual effort, other thanby operating other control means which may be located at a point remotefrom the rotary tongs.

Further objects and advantages of the invention will be apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a side elevational view with parts in section for greaterclarity and showing a power driven rotary tongs constructed inaccordance with this invention with the same being shown in inoperativeposition in full lines and in operative position in dotted lines;

FIG. 2 is a fragmentary top plan view with parts broken away and insection for greater clarity and showing the jaw structure for engagingthe pipe string;

FIG. 3 is a fragmentary sectional view taken on the line 3-3 of FIG. 2and showing a portion of the mecha nism for engaging the jaws with thepipe section to be rotated;

FIG. 4 is a side elevational view with ports broken away and in sectionfor greater clarity and showing the pipe engaging jaws, as well as thedrive mechanism for rotating one section of pipe with respect to theother;

FIG. 5 is a side elevational view with parts broken away and in sectionfor greater clarity and showing the flywheel utilized to impart torqueto the driving mechanism, together with means for limiting or adjustingthe torque transmitted thereby; and

FIG. 6 is a fragmentary sectional view showing another aspect of thetorque adjusting or limiting mechanism incorporated in the flywheelshown in FIG. 5.

With continued reference to the drawing, there is shown a power drivenrotary tons which may well comprise a base 10 mounted on a pedestal 11and if desired, the base It) may be provided with a sleeve 12surrounding the pedestal 11 in order to provide for rotation of the baseIt) with respect to the pedestal 11, although such movement is notnecessary unless it is desired to use the rotary tongs in one locationfor operation on several adjacent drill strings.

A carriage 13 is provided with elongated rails 14 which are slidablymounted on the base 10 in order to permit movement of the carriage 13transversely of the base 10 and pedestal 11. A hydraulic cylinder 15 maybe secured to the base 10 and slidable within the cylinder 15 is apiston 16 to which is connected a piston rod 17 which in turn isconnected through a suitable coupling means 18 with the carriage 13.Consequently, operation of the hydraulic cylinder 15 serves to move thecarriage l3 laterally of the base 10 from an inoperative position to anoperative position in alignment with a pipe string and in a manner to belater described.

With particular reference to FIG. 4, there is shown a fixed lower pipesection holding jaw 19 which may include a jaw body 20 mounted on thebase 16, the jaw body 20 having a generally U-shaped opening as shown inFIG. 2 for receiving a lower pipe section during operation of theapparatus. Pipe engaging jaw pieces 21 are carried by the lower jaw body20 and the jaw pieces 21 are connected to a yoke 22, the yoke 22 beingconnected to an arm 23 as shown in FIG. 2, and with the arm 23 beingconnected to the piston rod 24 of a hydraulic cylinder 25 pivotallymounted as at 26 on a bracket 27 secured to the base 1%. The jaw pieces21 may be loo-sely held in position by suitable spring means 28 as shownin FIG. 4. The particular manner of mounting and actuating the jawpieces 21 for engagement with the lower pipe section 29 is the same asfor the upper jaws and jaw pieces which will be presently described andsince the specific structure of such upper jaw pieces and the mountingtherefor is shown in FIG. 2, it is believed that a description thereofwill also suflice for a description of the specific mounting andoperation of the lower jaw pieces 21.

Again referring to FIGS. 2 and 4, an upper pipe section engaging jaw 30may well include an upper jaw body 31 having a generally U-shapedopening, as shown in FIG. 2, for receiving the upper pipe section 32 andprovided in the upper body 31 are oppositely extending tapered surfaces33 and 34 on opposite sides of the upper body 31 and pipe engaging upperjaw pieces 35 are provided with roller means 36 engaging the taperedsurfaces-33 and 34 for a purpose to be presently described. An upperyoke .37 is connected to the upper jaw pieces 35.

A master gear 38 is rotatably mounted on the lower body 20 by means ofrollers 39 and the master gear 38 frictionally engages the upper yoke 37to drive the same.

The upper body 30 is coupled to the master gear 38 by suitable slidingpin means 40 which permit rotation of the upper body 30 by the mastegear 38 and at the same time, permits vertical movement of the upperbody 35 as the upper pipe section 32 is screwed into or out of the lowerpipe section 29.

As best shown in FIG. 3, the upper yoke 37 is provided with a ratchettooth 41 and a plunger 42 is slidably mounted in the lower body 20 and apawl 43 is carried by the plunger 42 for engaging the tooth 41 on theupper yoke 37. The plunger 42 may be connected through a suitable rod orlinkage means 44 with a: hydraulic cylinder 45, FIGURE 4, which may beutilized for actuating the plunger 42 and for moving the pawl 43 intoand out of engagement with the ratchet tooth 41. The operation of thismechanism will be later described.

The master gear 38 may be driven through a gear train which may includethe gears 46, 47 and 48 which in turn are connected to a gear 451meshing with a pinion gear 50 mounted on a drive shaft 51 which iscoupled to a prime mover 52 which may be of any desired type, such as anelectric or hydraulic motor. As best shown in FIGS. 4 and 6, the driveshaft 53 of the prime mover 52 is coupled to a sleeve 54 by splines orother suitable coupling means 55 and the opposite end of sleeve 54 isprovided with splines 56 or other suitable means for coupling the sameto the drive shaft '51 carrying the pinion gear 50. Rotatably mounted onthe sleeve 54 by suitable bearings 57 is a flywheel 58 and insofar asthis mounting means is concerned, the flywheel 58 is freely rotatable onthe sleeve 54.

Fixed to the sleeve 54 below the flywheel 58 is a disk 59 and carried bythe disk 59 is an arcuate series of balls 60 which provide protuberancesprojecting above the up- -per surface of the disk 59 which theprotuberances 60 facing the lower surface of the flywheel 58. Aninclined bore 61 is provided in the flywheel 58 and disposed in the bore61 is a compression spring 62, the lower end of which engages a plunger63 which in turn engages a pawl .64 providing a detent projectingoutwardly of the lower surface of the flywheel 58 and engaging theprotuberances 60 on the disk 59. The opposite end of the spring 62engages the plug 65 slidably received in the bore 61 and the plug 65projects upwardly above the upper end surface of the flywheel 58 andengages a plate 66 carried by the flywheel 58 and the plate 66 may beadjusted to vary the tension on the spring 62 in order to vary the forceby which the detent 64 engages the protuberances 60. By reason of thisstructure, the flywheel 58 will transmit torque to the disk 59 and driveshaft 51 by engagement of the detent 64 with the protuberances 60 andthe degree of torque transmitted will be determined by the direction ofrotation of the flywheel 58, since by reason of the inclination of thebore 61, the detent 64 will be disengaged from the protuberances 60 moreeasily when rotating in one direction than in the other and thismechanism is so disposed as to transmit the minimum amount of torque fortightening the pipe string and the maximum amount of torque forloosening or unscrewing one section of the pipe string from the other.

.In order to stop the upper jaw body 30 in a neutral position with theU-shaped opening therein in proper position to be received around theupper section 32 of the pipe string, there may be provided a recess 67in the master gear 38 and a stop pin 68 is slidably mounted in the lowerbody member 20 and the stop pin 68 may be actuated by a fluid pressurecylinder 69 to move the same into and out of engagement with the recess67.

In operation, the hydraulic cylinder 15 may be actuated to move the base10 and mechanism carried thereby into alignment with the upper and lowerpipe sections 32 and 29 and in such a manner that the pipe sections willbe received within the upper and lower jaw bodies. The hydrauliccylinder 25 may then be actuated to move the lower jaw pieces 21 withrespect to the tapered surfaces in the lower jaw body 20 to engage suchjaw pieces 21 with the lower pipe section 29 to securely clamp and holdthe same against rotation. The prime mover 52 may be energized to rotatethe flywheel 58, drive shaft 51 and the gear train driving the mastergear 38 in order to rotate the upper jaw body 30* and the yoke 37 untilsuch time as this mechanism has obtained the desired rotational speed.At this time, the hydraulic cylinder 45 may be energized to actuate thelinkage or rod 44 which in turn actuates the plunger 42 to move the pawl43 into engagement with the ratchet tooth 41 thereby stopping rotationof the yoke 37 and upper jaw pieces 35 which will cause such jaw piecesto move with respect to the tapered surfaces 33 and 34 thereby movingthe jaw pieces 35 into clamping engagement with the upper pipe see tion32. The inertia of the flywheel 58 and rotating por tions of theapparatus will there-by rotate the upper pipe section 32 to screw thesame into firm engagement with the lower pipe section 29 and upon themaximum torque being applied to the upper pipe section 32, in the eventsuch maximum torque is exceeded, the detent 64 will move out ofengagement with the protuberances 60 thereby permitting the flywheel 58to rotate with respect to the disk 59 and drive shaft 51 which precludesbreakage of the apparatus due to an excess of torque being applied. Uponcompletion of the pipe rotating operation the cylinder 69 may beenergized to move the stop pin 68 into engagement with the recess 67 inthe master gear 38 thereby positioning the U-shaped opening in the upperjaw body 30 in proper alignment for the base 10 and apparatus carriedthereby to be moved transversely out of engagement with the pipesections 29 and 32.

While the. apparatus of this invention has been shown and described asoperating on a single pipe section, obviously, the base 10 and apparatuscarried thereby may be rotated about the pedestal 11 to position theapparatus for engagement with other adjacent pipe sections in order torotate the same for applying or separating pipe sections. It will,therefore, be seen that there has been provided by this invention arelatively simple, yet highly eflective power driven rotary tongs foroperating upon pipe sections and in which all lateral strain on the pipestring has been eliminated and in which the torque applied to the pipesection may be conveniently limited to a predetermined value.Furthermore, all of the operations of the apparatus of this inventionmay be conveniently controlled from a remote location and the use of theapparatus requires substantially no manual operations whatsoever, asidefrom operating the necessary controls.

It will be obvious to those skilled in the art that various changes maybe made in the invention without departing from the spirit and scopethereof and therefore the invention is not limited by that which isshown in the drawings and described in the specification, but only asindicated in the appended claims.

I claim:

1. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, hydraulic means formoving said carriage on said base, a fixed lower pipe section holdingjaw on said base and including a jaw body having a generally U-shapedopening for receiving said lower pipe section, oppositely extendingtapered surfaces on opposite sides of said body, pipe engaging jawpieces slidably engaging said surfaces, a yoke connected to said jawpieces, an arm extending from said yoke and hydraulic means connected tosaid arm for moving said yoke and jaw pieces in either direction withrespect to said surfaces to move said jaw pieces into clampingengagement with a lower section of pipe, an upper pipe section engagingjaw rotatably mounted on said base in alignment with said lower jaw andincluding an upper jaw body having a generally U- shaped opening forreceiving said upper pipe section, oppositely extending upper taperedsurfaces on opposite sides of said upper body, pipe engaging upper jawpieces slidably engaging said upper surfaces, an upper yoke connected tosaid upper jaw pieces, a master gear rotatably mounted on said lowerbody and frictionally engaging said upper yoke to drive the same, drivemeans connecting said upper body and said master gear, a ratchet toothon said upper yoke, a plunger slidably mounted on said lower body, apawl carried by said plunger, hydraulic means connected to said plungerfor moving said pawl into engagement with said tooth to stop rotation ofsaid upper yoke with respect to said master gear and upper body to movesaid upper jaw pieces into clamping engagement with said upper pipesection, a gear train for driving said master gear, a prime mover, adrive shaft connecting said prime mover and said gear train, a flywheelrotatably mounted on said drive shaft, a disk fixed to said drive shaftat one end of said flywheel, an arcuate series of protuberances on saiddisk facing said flywheel, a spring pressed detent in said flywheelreleasably engaging said protuberances to transmit torque from saidflywheel to said drive shaft, a recess in said master gear, a stop pinslidably mounted in said lower body for engaging said recess to stopsaid master gear in neutral position and hydraulic means for actuatingsaid stop pin.

2. Power driven rotary tongs as defined in claim 1, in which theengagement of said spring pressed detent with said protuberances may beadjusted to vary the torque transmitted by said flywheel.

3. Power driven rotary tongs as defined in claim 1, in which the torquetransmitted by said flywheel is different in one direction than in theother direction of rotation.

4. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, hydraulic means formoving said carriage on said base, .a fixed lower pipe section holdingjaw on said base and including a jaw body having a generally U-shapedopening for receiving said lower pipe section, oppositely extendingtapered surfaces on opposite sides of said body, pipe engaging jawpieces slidably engaging said surfaces, a yoke connected to said jawpieces, an arm extending from said yoke and hydraulic means connected tosaid arm for moving said yoke and said jaw pieces in either directionwith respect to said surfaces to move said jaw pieces into clampingengagement with the lower section of pipe, an upper pipe sectionengaging jaw rotatably mounted on said base in alignment with said lowerjaw and including an upper jaw body having a generally U-shaped openingfor receiving said upper pipe section, oppositely extending uppertapered surfaces on opposite sides of said body, pipe engaging upper jawpieces slidably engaging said upper surfaces, an upper yoke connected tosaid upper jaw pieces, a master gear rotatably mounted on said lowerbody and frictionally engaging said upper yoke to drive the same, drivemeans connecting said upper body and said master gear, a ratchet toothon said upper yoke, a plunger slidably mounted on said lower body, apawl carried by said plunger, hydraulic means connected to said plungerfor moving said pawl into engagement with said tooth to stop rotation ofsaid upper yoke with respect to said master gear and upper body to movesaid upper jaw pieces into clamping engagement with said upper pipesection, a gear train for driving said master gear, a prime mover, adrive shaft connecting said prime mover and said gear train, a flywheelrotatably mounted on said drive shaft, a disk fixed to said drive shaftat one end of said flywheel, an arcuate series of protuberances on saiddisk facing said flywheel and a spring pressed detent in said flywheelreleasably engaging said protuberances to transmit torque from saidflywheel to said drive shaft.

5. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, hydraulic means formoving said carriage on said base, a fixed lower pipe section holdingjaw on said base and including a jaw body having a generally U-shapedopening for receiving said lower pipe section, oppositely extendingtapered surfaces on opposite sides of said body, pipe engaging jawpieces slidably engaging said surfaces, a yoke connected to said jawpieces, an arm extending from said yoke and hydraulic means connected tosaid arm for moving said yoke and said jaw pieces in either directionwith respect to said surfaces to move said jaw-pieces into clampingengagement with a lower section of pipe, an upper pipe section engagingjaw rotatably mounted on said base in alignment with said lower jaw andincluding an upper jaw body having a generally U-shaped opening forreceiving said upper pipe section, oppositely extending upper taperedsurfaces on opposite sides of said upper body, pipe engaging upper jawpieces slidably engaging said upper surfaces, an upper yoke connected tosaid. upper jaw pieces, a master gear rotatably mounted on said lowerbody and frictionally engaging said upper yoke to drive the same, drivemeans connecting said upper body and said master gear, a ratchet toothon said upper yoke, a plunger slidably mounted on said lower body, apawl carried by said plunger, hydraulic means connected to said plungerfor moving said pawl into engagement with said tooth to stop rotation ofsaid upper yoke with respect to said master gear and upper body to movesaid upper jaw pieces into clamping engagement with said upper pipesection, a gear train for driving said master gear, a prime mover, adrive shaft connecting said prime mover and said gear train, a flywheelrotatably mounted on said drive shaft and means to transmit torque fromsaid flywheel to said drive shaft.

6. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, hydraulic means formoving said carriage on said base, a fixed lower pipe section holdingjaw on said base and including a jaw body having a generally U-shapedopening for receiving said lower pipe section, oppositely extendingtapered surfaces on opposite sides of said body, pipe engaging jawpieces slidably engaging said surfaces, a yoke connected to said awpieces, an arm extending from said yoke and hydraulic means connected tosaid arm for moving said yoke and said jaw pieces in either directionwith respect to said surfaces to move said jaw pieces into clamping engagement with a lower section of pipe, an upper pipe section engagingjaw rotatably mounted on said base in alignment with said lower jaw andincluding an upper jaw body having a generally U-shaped opening forreceiving said upper pipe section, oppositely extending upper taperedsurfaces on opposite sides of said upper body, pipe engaging upper jawpieces slidably engaging said upper surfaces, an upper yoke connected tosaid upper jaw pieces, a master gear rotatably mounted on saidlower bodyand frictionally engaging said upper yoke to drive the same, drive meansconnecting said upper body and said master gear, means to stop rotationof said upper yoke with respect to said master gear and upper body tomove said upper jaw pieces into clamping engagement with said upper pipesection, a gear train for driving said master gear, a prime mover, adrive shaft connecting said prime mover and said gear train, a flywheelrotatably mounted on said drive shaft and means to transmit torque fromsaid flywheel to said drive shaft.

7. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, means for movingsaid carriage on said base, a fixed lower pipe section holding jaw onsaid base and including a jaw body having a generally U-shaped openingfor receiving said lower pipe section, oppositely extending taperedsurfaces on opposite sides of said body, pipe engaging jaw piecesslidably engaging saidsurfaces, a yoke connected to said jaw pieces, anarm extending from said yoke and means connected to said arm for movingsaid yoke and said jaw pieces in either direction with respect to saidsurfaces to move said jaw pieces into clamping engagement with a lowersection of pipe, an upper pipe section engaging jaw rotatably mounted onsaid base in alignment with said lower jaw and including an upper jawbody having a generally U-shaped opening for receiving said upper pipesection, oppositely extending upper tapered surfaces on opposite sidesof said upper body, pipe engaging upper jaw pieces slidably engagingsaid upper surfaces, an upper yoke connected to said upper jaw pieces, amaster gear rotatably mounted on said lower body and frictionallyengaging said upper yoke to drive the same, drive means connecting saidupper body and said master gear, means to stop rotation of said upperyoke with respect to said master gear and upper body to move said upperjaw pieces into clamping engagement with said upper pipe section, a geartrain for driving said master gear, a prime mover, a drive shaftconnecting said prime mover and said gear train, a flywheel rotatablymounted on said drive shaft and means to transmit torque from saidflywheel to said drive shaft.

8. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, means for movingsaid carriage on said base, a fixed lower pipe section holding jaw onsaid base and including a jaw body having a gen eral-ly U-shaped openingfor receiving said lower pipe section, pipe engaging jaw pieces in saidbody and means for moving said jaw pieces into clamping engagement witha lower section of pipe, an upper pipe section engaging jaw rotatablymounted on said base in alignment with said lower jaw and including anupper jaw body having a generally U-shaped opening for receiving saidupper pipe section, oppositely extending upper tapered surfaces onopposite sides of said upper body, pipe engaging upper jaw piecesslidably engaging said upper surfaces, an upper yoke connected to saidupper jaw pieces, a master gear rotatably mounted on said lower body andfrictionally engaging said upper yoke to drive the same, drive meansconnecting said upper body and said master gear, means to stop rotationof said upper yoke with respect to said master gear and upper body tomove said upper jaw pieces into clamping engagement with said upper pipesection, a gear train for driving said master gear, a prime mover, adrive shaft connecting said prime mover and said gear train, a flywheelrotatably mounted on said drive shaft and means to transmit torque fromsaid flywheel to said drive shaft.

9. Power driven rotary tongs comprising a base, a carriage slidablymounted on said base for movement from an inoperative position to anoperative position in alignment with a pipe string, means for movingsaid carriage on said base, a fixed lower pipe section holding jaw onsaid base and including a jaw body having a generally U-shaped openingfor receiving said lower pipe section, pipe engaging jaw pieces in saidbody and means for moving said jaw pieces into clamping engagement witha lower section of pipe, an upper pipe section engaging jaw rotatablymounted on said base in alignment with said lower jaw and including anupper jaw body having a generally U-shaped opening for receiving saidupper pipe section, pipe engaging upper jaw pieces carried by said upperbody, a master gear rotatably mounted on said lower body, drive meansconnecting said upper body and said master gear, means to move saidupper jaw pieces into clamping engagement with said upper pipe section,a gear train for driving said master gear, a prime mover, a drive shaftconnecting said prime mover and said gear train, a flywheel rotatablymounted on said drive shaft and means to transmit torque from saidflywheel to said drive shaft.

References Cited in the file of this patent UNITED STATES PATENTS2,450,934 Calhoun Oct. 12, 1948 2,509,854 Wilson May 30, 1950 2,518,398Stone Aug. 8, 1950 2,544,639 Calhoun Mar. 13, 1951 2,615,681 True Oct.28, 1952 2,639,894 Smith May 26, 1953 2,646,966 Lindberg July 28, 19532,668,689 Cormany Feb. 9, 1954 2,737,839 Paget Mar. 13, 1956 2,784,626Paget Mar. 12, 1957 2,850,929 Crookston et al. Sept. 9, 1958 2,862,690Mason Dec. 2, 1958 2,871,743 Kelley Feb. 3, 1.959 2,923,192 Montgomeryet al. Feb. 2, 1960

